Issue #3307903 Added missing utility method

    ));

  }

  /**

   * Converts a Unix timestamp to an ISO 8601 date as expected by the SP-API.

   *

   * @param int $timestamp

   *   The Unix timestamp to convert.

   *

   * @return string

   *   The time in ISO 8601 format and in UTC timezone.

   *

   * @I Validate that the input is a Unix timestamp

   *    type     : bug

   *    priority : normal

   *    labels   : validation

   */

  public static function timestampToIso8601($timestamp) {

    $datetime = new \DateTime('now', new \DateTimeZone('UTC'));

    $datetime->setTimestamp($timestamp);

    return $datetime->format('Y-m-d\TH:i:s') . 'Z';

  }

}